Ischaemic heart disease and stroke mortality by specific coal type among non-smoking women with substantial indoor air pollution exposure in China

Background: Lifetime use of bituminous ('smoky') coal is associated with nearly a 100-fold higher risk of lung cancer mortality compared with anthracite ('smokeless') coal use in rural Xuanwei, China, among women. Risk of mortality from ischaemic heart disease (IHD) and stroke for these coal types has not been evaluated. Methods: A cohort of 16 323 non-smoking women in Xuanwei, who were lifetime users of either smoky or smokeless coal, were followed up from 1976 to 2011. We estimated hazard ratios (HRs) and 95% confidence intervals (CI) to evaluate lifetime use of coal types and stoves in the home in relation to risk of IHD and stroke mortality. Results: Among lifetime users of smokeless coal, higher average exposure intensity (>= 4 tons/year vs <2.5 tons/year, HR = 7.9, 95% CI = 3.5-17.8; P-trend =<0.0001) and cumulative exposure (>64 ton-years vs <= 28 ton-years, HR = 6.5, 95% CI = 1.5-28.3; P-trend =0.003) during follow-up and over their lifetime was associated with increased IHD mortality, and ventilated stove use dramatically reduced this risk (HR = 0.2, 95% CI 0.1-0.5). Higher cumulative exposure to smoky coal during follow-up showed positive associations with IHD mortality, but the evidence for other metrics was less consistent compared with associations with smokeless coal use. Conclusions: Higher use of smokeless coal, which is burned throughout China and is generally regarded to be a cleaner fuel type, is associated with IHD mortality. Use of cleaner fuels or stove interventions may be effective in reducing the increasing burden of IHD in developing regions that currently rely on smokeless coal for cooking and heating.